This invention relates to a heterogeneous cellular network.
Currently, a conventional cellular network (hereinafter sometime referred to as homogeneous cellular network) including only one type of base station is widely used. A cellular network (hereinafter also referred to as “heterogeneous cellular network”) including many types of base stations has also been researched and developed, and is being gradually applied and popularized.
FIG. 9 is a block diagram illustrating a configuration of the heterogeneous cellular network. In the heterogeneous cellular network illustrated in FIG. 9, there are four macro base stations (Macro BS) MBS and eight micro base stations mBS. Here, the micro base station is a generic term for mini type base stations, which are different from the macro base station, including, for example, femto base stations (Femto BS), pico base stations (pico BS), micro base stations (Micro BS), and the like. Further, MC (also referred to as “macro cell”) represents a cell covered by the macro base station MBS, and mC (also referred to as “micro cell”) represents a cell covered by the micro base station mBS.
Usually, the transmitting power of the micro base station is much lower than that of the macro base station, the coverage area of the micro cell is much smaller than that of the macro cell, and a probability that the number of users of the micro cell is smaller than that of the macro cell is high. However, in the related art, same frequency bands may be allocated to the micro base station and the macro base station, or in order to reduce interference between cells, different frequency bands may also be allocated to the micro base station and the macro base station. In addition, the frequency bands to be allocated to the micro base station and the macro base station are often in either state of being used up completely or being completely off.
Thus, when the same frequency bands are allocated to the micro base station and the macro base station, the micro base station allocates all of the frequency bands to the users in the micro cell. As a result, there is a fear of providing the so-called excess service of more than a required number of frequency bands for the users. For that reason, there exist problems in that not only the resources are wasted due to providing the excess service, but also the interference between cells becomes stronger because the micro base station and the neighboring base station use the same frequency bands, resulting in reducing the network capacity.
In order to reduce the interference, US2012/0157108A1 discloses a technology of a fractional frequency reuse mechanism for a heterogeneous cellular network. The mechanism is a direct extension of the fractional frequency reuse mechanism in the traditional homogeneous cellular network, i.e., allocating resources based on the user's position information. Further, WO2012/106987A1 discloses a solution of reducing the interference, in which the base station and the micro node in a heterogeneous cellular network use different position information.